Five to seven is the modal onset age of GTD. This patient’s GTD signs are motor and vocal tics, with no choreiform movements

Huntington’s disease

presents with rigidity, dystonia, dementia (actually, mental retardation) or mood disorder. Choreiform movements are rare in children with Huntington’s

Wilson’s disease

typically begins at age 16 and is characterized by dementia, cirrhosis, corneal Kayser-Fleischer rings, rigidity, akinesia, dystonia and wing-beating tremor—a coarse tremor centering on the shoulders in which patients move their arms as though they were trying to fly.

Parkinson’s disease

begin before 21 but that is extremely rare

juvenile variants

Huntington’s, Wilson’s and Parkinson’s diseases have very rare juvenile variants

Attention deficit hyperactivity disorder

characterized by being unable to sit still and talking out of turn, but it is not associated with tics unless a tic disorder patient also has ADHD

characterized by episodes of mania or depression during which the patient may also have findings (e.g., formal thought disorder, first rank symptoms, emotional blunting) more typical of schizophrenia than mood disorder and, most important, the patient has had mood-incongruent hallucinations or delusions lasting two or more weeks

Huntington’s disease, Sydenham’s chorea, neuroacanthocytosis, post-encephalitic Parkinson’s disease, manganese toxicity, carbon monoxide toxicity) can present with similar symptoms, although in these conditions the clinical picture is more atypical than in primary OCD.

characterized by one or more periods lasting two weeks or more of hallucinations or delusions not associated with episodes of mania or major depression and, sometimes, signs of schizophrenia (e.g., formal thought disorder, first rank symptoms or emotional blunting) that occur during episodes of mania or major depression.

Schizophrenia

which cannot be diagnosed in the presence of a major mood disorder, is characterized by emotional blunting; formal thought disorder; first rank signs; and, early in the illness, delusions or hallucinations.

Delusional disorder

characterized by systematized delusions in the absence of mood disorder, first rank symptoms, formal thought disorder or emotional blunting.

Cyclothymic disorder

mild variant of bipolar disorder characterized by chronic low-grade mood swings including hypomania or depression, lasting most of the time for at least two years, with well periods not exceeding two months and without any manic or major depressive episodes.

Sensitization

characterized by progressively longer mood disorder episodes and progressively shorter remissions, with progressively less stress—eventually, no stress at all—required to trigger episodes.

Adjustment disorder

characterized by marked distress and impaired social functioning in response to an identifiable stressor, but where symptoms are not severe enough to meet criteria for another disorder. Except for military acute inpatient units, try to avoid diagnosing adjustment disorder because a more severe or chronic disorder is more likely.

bipolar II disorder

the patient has one or more major depressive episodes and one or more hypomanic episodes, but no manic episodes. Bipolar patients have a 10-15% lifetime suicide risk.

Antisocial personality disorder

characterized by childhood conduct disorder followed by lifelong adulthood selfishness; callousness; lack of concern for others; lack of remorse for hurtful behaviors; impulsivity, high novelty seeking and low harm avoidance; law-breaking; inability to maintain a job or marriage; low reward dependence; irritability; fighting or violence; lying or using an alias.

Somatization disorder

characterized by four or more medically-unexplained pain symptoms, two or more medically-unexplained gastrointestinal symptoms other than pain, and one medically-unexplained sexual symptom, one pseudoneurologic symptom, all spread over multiple years with onset before age 30.